DNA Structure and Gene Function
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Questions and Answers

What percentage of the human genome is believed to code for proteins or functional RNA molecules?

  • Around 50%
  • Exactly 25%
  • More than 75%
  • Less than 5% (correct)

    • Telomeres are located at the ends of chromosomes and are protective sequences.

    True (A)

    What are the small repeating units formed by DNA wrapped around histone proteins called?

    nucleosomes

    The _____ is the structure that attaches sister chromatids to the mitotic spindle during cell division.

    <p>centromere</p> Signup and view all the answers

    Match the following parts of the chromosomal structure with their functions:

    <p>Replication Origins = Sites where DNA replication begins Telomeres = Protective sequences at chromosome ends Centromeres = Attach sister chromatids to the spindle Nucleosomes = Basic unit of DNA packaging</p> Signup and view all the answers

    What is required for chromatin remodeling complexes to function?

    <p>ATP (C)</p> Signup and view all the answers

    Chromatin must remain static at all times to maintain gene function.

    <p>False (B)</p> Signup and view all the answers

    What role do histone chaperones play in chromatin dynamics?

    <p>They collaborate with remodeling complexes to reposition or remove histones.</p> Signup and view all the answers

    What pairs with adenine (A) in DNA?

    <p>Thymine (T) (C)</p> Signup and view all the answers

    DNA exists as a single strand in its natural form.

    <p>False (B)</p> Signup and view all the answers

    What is the structure of DNA that allows it to store genetic information?

    <p>Double helix</p> Signup and view all the answers

    During DNA replication, a DNA strand serves as a template for synthesizing a __________ strand.

    <p>complementary</p> Signup and view all the answers

    Match the following components with their descriptions:

    <p>Gene = Sequence of nucleotides that produce proteins or RNA Exon = Coding region of a gene Intron = Non-coding region of a gene Chromosome = Single long DNA molecule containing many genes</p> Signup and view all the answers

    In eukaryotic cells, where is DNA primarily located?

    <p>Nucleus (B)</p> Signup and view all the answers

    During cell division, genetic information can be inaccurately passed on if DNA replication is flawed.

    <p>True (A)</p> Signup and view all the answers

    What is the complete set of genetic information in an organism called?

    <p>Genome</p> Signup and view all the answers

    What does position effect variegation demonstrate about gene expression?

    <p>It can be altered by chromatin structure. (B)</p> Signup and view all the answers

    Centromeric chromatin is not needed for proper chromosome segregation.

    <p>False (B)</p> Signup and view all the answers

    What is the main role of epigenetic cell memory?

    <p>To allow cells to retain their specific states without altering the DNA sequence.</p> Signup and view all the answers

    In multicellular organisms, the ____________ system is crucial for maintaining distinct cell states and functions.

    <p>epigenetic memory</p> Signup and view all the answers

    How often does mutation occur in a typical eukaryotic lineage?

    <p>1 out of every 1,000 nucleotides every million years (C)</p> Signup and view all the answers

    The genomes of humans and chimpanzees show many differences due to their evolutionary divergence.

    <p>False (B)</p> Signup and view all the answers

    Match the following concepts with their descriptions:

    <p>Position effect variegation = Gene expression affected by proximity to heterochromatin Centromeric chromatin = Necessary for chromosome segregation Epigenetic memory = Retention of cell states without DNA alteration Genome comparison = Study of nucleotide sequence differences among species</p> Signup and view all the answers

    What have nucleotide sequence comparisons revealed about human and chimpanzee genomes?

    <p>They reveal that the genes are nearly identical and the order of genes on their chromosomes is mostly unchanged.</p> Signup and view all the answers

    What is the primary function of nuclear subcompartments?

    <p>Coordinating specific cellular processes (B)</p> Signup and view all the answers

    During mitosis, gene expression is highly active.

    <p>False (B)</p> Signup and view all the answers

    What role do histone modifications play during the condensation process of chromosomes?

    <p>They facilitate the tighter packing of chromatin.</p> Signup and view all the answers

    Nuclear subcompartments like the __________ are involved in ribosome synthesis.

    <p>nucleolus</p> Signup and view all the answers

    Match the following nuclear structures with their main function:

    <p>Nucleolus = Ribosome synthesis Cajal bodies = RNA splicing Chromatin = DNA packaging during mitosis Nuclear envelope = Organizing nuclear components</p> Signup and view all the answers

    What occurs to chromatin during mitosis?

    <p>It undergoes significant condensation (C)</p> Signup and view all the answers

    The condensation process of chromosomes reduces the DNA length by a factor of ten.

    <p>True (A)</p> Signup and view all the answers

    Why is the orderly segregation of chromosomes during mitosis important?

    <p>To ensure each daughter cell receives the correct number of chromosomes.</p> Signup and view all the answers

    What is the primary form of chromatin that consists of loosely packed nucleosomes during interphase?

    <p>Euchromatin (A)</p> Signup and view all the answers

    Chromosomes are extensively intertwined with each other during interphase.

    <p>False (B)</p> Signup and view all the answers

    What role does heterochromatin play in gene expression?

    <p>Gene silencing and structural chromosome integrity</p> Signup and view all the answers

    During interphase, chromosomes are generally __________, making their structure difficult to observe.

    <p>decondensed</p> Signup and view all the answers

    Which type of chromosome provides insight into chromatin organization during interphase?

    <p>Lampbrush chromosomes (C)</p> Signup and view all the answers

    Match the following terms with their descriptions:

    <p>Euchromatin = Loosely packed, accessible for transcription Heterochromatin = Tightly packed, gene silencing Lampbrush chromosomes = Specialized chromosomes in oocytes Polytene chromosomes = Found in insect secretory cells</p> Signup and view all the answers

    What are chromatin loop domains?

    <p>Distinct sections of DNA compacted through additional folding.</p> Signup and view all the answers

    Heterochromatin is found only around centromeres and near telomeres.

    <p>False (B)</p> Signup and view all the answers

    Study Notes

    DNA Structure and Function

    • DNA is a double helix composed of two strands of nucleotides.
    • The strands are complementary and antiparallel, meaning they run in opposite directions.
    • Adenine (A) pairs with thymine (T), and guanine (G) pairs with cytosine (C).
    • DNA replication uses one strand as a template to make a complementary strand, ensuring accurate genetic information transfer.
    • The genome is the complete set of DNA in an organism, including instructions for RNA and protein synthesis.
    • In eukaryotes, DNA is located in the nucleus, a compartment that protects and regulates DNA processes.

    Understanding Genes

    • A gene is a segment of DNA that codes for a protein, structural or regulatory RNA.
    • Eukaryotic protein-coding genes have alternating introns (non-coding) and exons (coding) regions.
    • Chromosomes consist of a single long DNA molecule with genes arranged linearly.
    • The human genome is composed of 3.2 billion nucleotide pairs, organized into 46 chromosomes, two of which are sex chromosomes.

    Chromatin Structure and Organization

    • DNA is tightly packaged with histone proteins, forming nucleosomes.
    • Nucleosomes are spaced about 200 nucleotide pairs apart in a repeating pattern.
    • Nucleosomes are further packed into chromatin fibers (30-nm) aided by histone H1.
    • Chromatin must undergo dynamic changes for gene expression, replication, and repair.
    • Chromatin remodeling complexes use ATP to alter chromatin structure.
    • Histone chaperones work with remodeling complexes to modify nucleosome cores.

    Epigenetic Regulation

    • Heterochromatin, a tightly packed form of chromatin, is largely inaccessible for gene expression and plays a role in gene silencing and chromosomal stability.
    • Euchromatin is a loosely packed form of chromatin that is more accessible for transcription.
    • Position effect variegation demonstrates that condensed chromatin can be inherited across cell generations.
    • Epigenetic memory allows cells to retain specific states (e.g., differentiation) without DNA sequence alterations.
    • Epigenetic mechanisms are vital for maintaining cell identity and function in multicellular organisms.

    Chromosome Structure in Interphase

    • Interphase chromosomes are decondensed, making their structure less observable, though exceptions exist (lampbrush, polytene).
    • Chromosomes are divided into chromatin loop domains, representing compacted sections of DNA.
    • When genes in loops are activated, the loop temporarily unfolds.
    • Chromosomes occupy discrete territories within the nucleus to prevent entanglement and facilitate proper gene regulation.

    Nuclear Organization and Function

    • The nucleus has specialized regions called nuclear subcompartments that concentrate relevant proteins and RNAs.
    • Nuclear subcompartments, like the nucleolus and Cajal bodies, facilitate ribosome synthesis and RNA splicing.

    Chromosomes During Mitosis

    • Mitosis involves significant chromosome condensation, which begins in the early M phase.
    • Histone modifications contribute to chromosome condensation, facilitating the tight packaging of DNA.
    • Additional proteins are needed for complete chromosome condensation, reducing DNA length by a factor of ten.
    • Chromosome condensation is crucial for the orderly segregation of chromosomes into daughter cells.

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